webos.inc: Remove '()/' chars from WEBOS_DISTRO_BUILD_CODENAME

:Release Notes:
Now with branch name included in image names it can cause build
errors when the branch contains some characters with special
meaning in shell, don't remove it only at the beginning or end of the
string -> replace strip with translate.

:Detailed Notes:
Noticed when builds started to fail with build-webos branch set to
'jansa/dylan' do_rootfs fails with:
 | tar: /OE/webos/build/build-webos-dylan/BUILD/deploy/images/
   webos-image-devel-qemux86-jansa/dylan-20140218104419.rootfs.tar:
   Cannot open: No such file or directory

:Testing Performed:
Only build tested.

:QA Notes:
No change to image.

:Issues Addressed:
[ANG-329] Ongoing metadata improvement/cleanup work

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@lge.com>

Change-Id: I3c66d9170d7ce98eb977e1c9901ffcb30064d4e6
Reviewed-on: https://g2g.palm.com/4720
Reviewed-by: DCO Verification
Reviewed-by: Martin Jansa <Martin.Jansa@lge.com>
Reviewed-by: Build Verification
Tested-by: Martin Jansa <Martin.Jansa@lge.com>
Reviewed-by: Susan Montooth <susan.montooth@lge.com>